<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>Document</title>
  <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
</head>

<body>
  <div id="app">
    <div>{{counter}}</div>
    <button @click="increment">+</button>
    <button @click="decrement">-</button>
  </div>

  <script>
    const app = new Vue({
      el: "#app",
      data: {
        counter: 0,
      },
      methods: {
        increment() {
          this.counter++;
        },
        decrement() {
          this.counter--;
        },
      },
    });
  </script>
</body>

</html>